Lithium-ion secondary batteries and other non-aqueous electrolyte secondary batteries have become increasingly important as power supplies installed in vehicles or as batteries for PCs and mobile devices, etc. In particular, for their abilities to provide high energy density while being lightweight, lithium-ion secondary batteries are suitable as high-power power supplies installed in vehicles.
In a non-aqueous electrolyte secondary battery such as lithium-ion secondary battery and the like, components (e.g. a supporting electrolyte, non-aqueous solvent) in the non-aqueous electrolyte solution may partially decompose during charging to form a layer (solid electrolyte interphase layer, or “SEI layer” hereinafter) on the surface of the negative electrode active material. The SEI layer may comprise a layer of an organic substance such as ROCO2Li (R is an organic group), etc., or a layer of an inorganic substance such as LiF, Li2O, etc. Such an SEI layer may be formed in excess when the battery is stored in a charged stated or when charging and discharging are repeated, possibly resulting in increased negative electrode resistance and giving rise to issues of decreased battery performance.
To deal with such problems, it has been suggested to include various additives in non-aqueous electrolyte solutions used in fabricating secondary batteries. For example, Japanese Patent Application Publication Nos. 2011-34893 and 2007-165125 disclose non-aqueous electrolyte solutions comprising oxalatoborate-based compounds (e.g. lithium bis(oxalate)borate).